This core is central to 4 of the projects in this proposal. Given the intensity of use of transgenic and knockout mice in these projects it is justified to consolidate this into a single core. This will facilitate the timely production and dissemination of mice, and ensure a higher degree of quality control. In addition, this core will perform all DNA and blastocyst injections, maintain ES cells, and carry out cryopreservation. Given the plethora of mice to be produced the cryopreservation capability is warranted (assuming no such facility already exists Columbia).